The disclosure relates generally to distributed antenna systems (DAS), and more particularly to techniques for measuring gain within the DAS.
Wireless customers are increasingly demanding digital data services, such as streaming video signals. At the same time, some wireless customers use their wireless communication devices in areas that are poorly serviced by conventional cellular networks, such as inside certain buildings or areas where there is little cellular coverage. One response to the intersection of these two concerns has been the use of DASs. A DAS is a wireless communications distribution system. A DAS includes a plurality of remote antenna units (RAUs) each configured to receive and transmit communications signals to client devices within the antenna range of the RAUs. A DAS can be particularly useful when deployed inside buildings or other indoor environments where the wireless communication devices may not otherwise be able to effectively receive radio frequency (RF) signals from a source.
In this regard, FIG. 1 illustrates distribution of communications services to remote coverage areas 100(1)-100(N) of a DAS 102, wherein ‘N’ is the number of remote coverage areas. These communications services can include cellular services, wireless services, such as RF identification (RFID) tracking, Wireless Fidelity (Wi-Fi), local area network (LAN), and wireless LAN (WLAN), wireless solutions (Bluetooth, Wi-Fi Global Positioning System (GPS) signal-based, and others) for location-based services, and combinations thereof, as examples. The remote coverage areas 100(1)-100(N) may be remotely located. In this regard, the remote coverage areas 100(1)-100(N) are created by and centered on RAUs 104(1)-104(N) connected to a head-end equipment (HEE) 106 (e.g., a head-end controller, a head-end unit, or a central unit). The HEE 106 may be communicatively coupled to a signal source 108, for example, a base transceiver station (BTS) or a baseband unit (BBU). In this regard, the HEE 106 receives downlink communications signals 110D from the signal source 108 to be distributed to the RAUs 104(1)-104(N). The RAUs 104(1)-104(N) are configured to receive the downlink communications signals 110D from the HEE 106 over a communications medium 112 to be distributed to the respective remote coverage areas 100(1)-100(N) of the RAUs 104(1)-104(N). In a non-limiting example, the communications medium 112 may be a wired communications medium, a wireless communications medium, or an optical fiber-based communications medium. Each of the RAUs 104(1)-104(N) may include an RF transmitter/receiver (not shown) and a respective antenna 114(1)-114(N) operably connected to the RF transmitter/receiver to wirelessly distribute the communications services to client devices 116 within the respective remote coverage areas 100(1)-100(N). The RAUs 104(1)-104(N) are also configured to receive uplink communications signals 110U from the client devices 116 in the respective remote coverage areas 100(1)-100(N) to be distributed to the signal source 108. The size of each of the remote coverage areas 100(1)-100(N) is determined by amount of RF power transmitted by the respective RAUs 104(1)-104(N), receiver sensitivity, antenna gain, and RF environment, as well as by RF transmitter/receiver sensitivity of the client devices 116. The client devices 116 usually have a fixed maximum RF receiver sensitivity, so that the above-mentioned properties of the RAUs 104(1)-104(N) mainly determine the size of the respective remote coverage areas 100(1)-100(N).
With continuing reference to FIG. 1, when the DAS 102 is configured to operate based on frequency division duplexing (FDD), the downlink communications signals 110D and the uplink communications signals 110U are communicated between the HEE 106 and the RAUs 104(1)-104(N) over downlink path(s) 118 and uplink path(s) 120, respectively. Since isolation between the downlink path(s) 118 and the uplink path(s) 120 may be limited, energy from the downlink path(s) 118 may leak into the uplink path(s) 120 and subsequently loop back to the downlink path(s) 118, thus causing the downlink communications signals 110D to gain extra energy. This extra energy gain resulted from energy leaked from the downlink path(s) 118 to the uplink path(s) 120 and looped back to the downlink path(s) 118 is hereinafter referred to as a loop gain. The loop gain can distort the downlink communications signals 110D. As a result, under certain gain and phase shift conditions (e.g., conditions according to the Barkhausen stability criterion), the downlink communications signals 110D and the uplink communications signals 110U in the DAS 102 may start oscillating. As a result, the DAS 102 may become unstable.
By designing and configuring the DAS 102 based on the generic loop gain, it is possible to minimize distortions to the downlink communications signals 110D resulting from the energy feedback, thus enabling stable operations of the DAS 102. Generic loop gain is defined in this context as a worst-case loop gain of the DAS 102. In this regard, the generic loop gain is defined based on the assumptions that the number of RAUs 104(1)-104(N) is large, and isolations between the downlink path(s) 118 and the uplink path(s) 120 (and vise versa) are minimal. However, by designing and configuring the DAS 102 based on the worst-case loop gain, it may lead to under-configuration and underutilization of the DAS 102.
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinency of any cited documents.